Stable isocyanate formulations

ABSTRACT

The pot life of an isocyanate formulation is controlled by including a chain extender having (a) at least two secondary amine groups, (b) no primary amine groups, and (c) a reactivity low enough that the chain extender will not react sufficiently with isocyanate groups present in the isocyanate formulation to increase the viscosity of the isocyanate formulation to more than 2000 mPa·s within 5 seconds in the isocyanate formulation.

BACKGROUND OF THE INVENTION

The present invention relates to stable isocyanate formulations, to aprocess for the production of such stable isocyanate formulations and toa process for the production of polyurethanes from such stableisocyanate formulations. A key feature of the present invention is theuse of a secondary amine-containing chain extender.

Processes for the production of polyurethanes are known. In theseprocesses, two reactive components are generally combined shortly beforethe polyurethane is to be formed. One of these components is generally apolyisocyanate and the other is composed of at least oneisocyanate-reactive material such as a polyol. Either of thesecomponents may include additives such as catalysts, chain extenders,cross-linking agents, surfactants, blowing agents, etc. Frequently,these additives are included in the polyol component. However, in caseswhere the additive may be highly reactive with one or more materialsincluded in the isocyanate-reactive component, that additive is oftenincluded in the isocyanate component. Chain extenders containing aminegroups are examples of materials that may be included in the isocyanatecomponent.

Amine chain extenders are commonly used in polyurethane-forming reactionmixtures. See, for example, U.S. Pat. Nos. 5,608,000 and 5,637,639. Oneof the advantages of amine chain extenders is their high reactivity.However, processing problems are encountered with amine chain extendershaving a reactivity which is so high that the isocyanate does not havesufficient time to react with other components present. This undesirablepre-reaction adversely affects the polyurethane product.

It would therefore be advantageous to develop a means for controllingthe degree of reactivity of an amine chain extender to such an extentthat a significant degree of pre-reaction at the expense of othermaterials present in the chain extender-containing component does notoccur before that component is combined with other reactive materials.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method forcontrolling the extent to which an amine chain extender present in anisocyanate formulation reacts with isocyanate groups present in thatformulation prior to initiation of the desired reaction.

It is another object of the present invention to provide a stableisocyanate formulation containing an amine chain extender.

It is a further object of the present invention to provide a process formaking a stable isocyanate formulation containing an amine chainextender.

These and other objects which will be apparent to those skilled in theart are accomplished by including an amine chain extender having noprimary amine groups present therein, having at least two secondaryamine groups, and having a low reactivity towards isocyanate groups inan isocyanate formulation. As used herein, “low reactivity” means thatthe secondary amine group will not react with an isocyanate groupsufficiently to cause the viscosity of the isocyanate to increase tomore than 2,000 mPa·s (at 25° C.) in less than 5 seconds. In the presentapplication, it is to be understood that “isocyanate formulation” meansat least one isocyanate and may optionally include other additives.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to stable polyisocyanate formulationscontaining an amine chain extender that contains no primary aminegroups, has at least two secondary amine groups and a low reactivitywith isocyanate groups. These polyisocyanate formulations areparticularly useful for the production of polyurethanes.

The polyisocyanates which may be used to produce the stable formulationsof the present invention include any of the known diisocyanates,polyisocyanates, prepolymers having at least two terminal isocyanategroups and modified diisocyanates and polyisocyanates. Examples ofsuitable isocyanates include: any of the isomers of toluene diisocyanateand mixtures thereof (“TDI”); diphenylmethane diisocyanate (“MDI”);polyphenylene polymethylene polyisocyanate (“PMDI”); hexamethylenediisocyanate (“HDI”); isophorone diisocyanate (“IPDI”); anddicyclohexylmethane 4,4′-diisocyanate. Particularly preferredisocyanates are HDI, IPDI, TDI, MDI and dicyclohexylmethane4,4′-diisocyanate.

Prepolymers having at least two terminal isocyanate groups useful in thepractice of the present invention may be prepared by any of thetechniques known to those in the art. Suitable prepolymers willgenerally have an NCO content of from about 15 to about 42%, preferablyfrom about 20 to about 35%. Such prepolymers are typically prepared byreacting an isocyanate with an isocyanate-reactive material in an amountsuch that a less than stoichiometric amount of isocyanate reactivematerial is used. Preferred prepolymers for use in the present inventioninclude polyether polyol prepolymers and polyester polyol prepolymers.

Modified diisocyanates and polyisocyanates suitable for use in thepractice of the present invention include: allophanate-modifiedisocyanates, particularly those prepared from monohydroxyl, dihydroxyland trihydroxyl compounds; biuret-modified isocyanates; and trimers.Methods for producing such modified diisocyanates and polyisocyanatesare known to those in the art.

Processes for producing the secondary amine chain extenders suitable foruse in the present invention are known. In one suitable method, analcohol in which the hydrogen of the hydroxyl group has been replacedwith a good leaving group (e.g., a mesylate or chloride group) isreacted with a primary amine to form the secondary amine. Suitablealcohols include any compound containing at least 2 hydroxyl groups. Thealcohol may have a hydrocarbon or an ether backbone. Preferred alcoholsinclude: 1,4-cyclohexane dimethanol, 2,2-dimethyl-1,3-propanediol,triethylene glycol and tripropylene glycol.

Primary amines that may be used to produce the chain extenders used inthe present invention include: tert-octylamine, 2-ethylhexylamine,cyclohexylamine, 2-amino-2-methylpropane, 1-octylamine, 1-butylamine,1-propylamine, aniline and toluidine. Preferred primary amines include:tert-octylamine, 2-ethylhexyl amine, and cyclohexylamine.

The amine chain extenders used in the present invention arecharacterized by: (1) the absence of primary amine groups; (2) thepresence of at least two secondary amine groups; and (3) a lowreactivity with isocyanate groups. The amine chain extenders can not beso reactive with the isocyanate being used that the viscosity of theisocyanate with which it is combined will increase in viscosity togreater than 2,000 mPa·s (at 25° C.) in less than 5 seconds. It ispreferred that the chain extender have a reactivity such that theisocyanate viscosity does not exceed 2,000 mPa·s (at 25° C.) for atleast 10 seconds, most preferably at least 15 seconds.

Examples of amine chain extenders that are useful in the practice of thepresent invention include those represented by the formula

R¹N R²—X—N R³R⁴  (I)

in which

R¹ represents an alkyl group having from 1 to 18 carbon atoms,preferably from 1 to 12 carbon atoms, most preferably from 4 to 8 carbonatoms, a cycloalkyl group having from 3 to 18 carbon atoms, preferablyfrom 3 to 12 carbon atoms, most preferably 6 carbon atoms, or an arylgroup having from 4 to 18 carbon atoms, preferably from 4 to 12 carbonatoms, most preferably from 6 to 10 carbon atoms,

R² represents hydrogen,

R³ represents an alkyl group having from 1 to 18 carbon atoms,preferably from 1 to 12 carbon atoms, most preferably from 4 to 8 carbonatoms, a cycloalkyl group having from 3 to 18 carbon atoms, preferablyfrom 3 to 12 carbon atoms, most preferably 6 carbon atoms, or an arylgroup having from 4 to 18 carbon atoms, preferably from 4 to 12 carbonatoms, most preferably from 6 to 12 carbon atoms,

R⁴ represents hydrogen,

X represents an alkyl group having from 1 to 16 carbon atoms, preferablyfrom 1 to 12 carbon atoms, most preferably from 1 to 8 carbon atoms, anaryl group having from 6 to 14 carbon atoms, preferably from 6 to 12carbon atoms, most preferably from 6 to 10 carbon atoms, or an ethergroup composed of at least one oxygen and two carbon atoms, preferablyone oxygen and four carbon atoms, most preferably two oxygen atoms and 6carbon atoms.

In the practice of the present invention, the chain extender is usuallyincluded in the isocyanate formulation in an amount such that theequivalent ratio of secondary amine groups to isocyanate groups is fromabout 1 to about 3, preferably from about 1 to about 2, most preferablyfrom about 1 to about 1.

The chain extender required in the practice of the present invention maybe incorporated into the isocyanate formulation by simple mixing or byany other technique known to those skilled in the art. After the chainextender has been added to the isocyanate, however, it is preferred thatthe isocyanate formulation be maintained at a temperature of at least50° C. In some cases, it is advantageous to agitate or stir theisocyanate formulation at regular intervals.

The isocyanate formulations of the present invention may be reacted withany of the isocyanate-reactive materials known to those in the art.Suitable isocyanate reactive materials include polyols such as polyetherpolyols and polyester polyols, and polyamines such as polyetherpolyamines and polyalkyl polyamines.

Having thus described our invention, the following Examples are given asbeing illustrative thereof. All parts and percentages given in theseExamples are parts by weight and percentages by weight, unless otherwise indicated.

EXAMPLES Preparation of Chain Extenders

Chain extenders were prepared by the following procedure. 3 mols of theprimary amine indicated in Table 1 below were reacted with 1 mol of themesylate of the alcohol identified in Table 1 in a flask at 150° C. for2 hours. The solution was then cooled and neutralized with 50% sodiumhydroxide. Excess primary amine and water were vacuum stripped from themixture and the product secondary amine was filtered and vacuum

TABLE 1 EXTENDER ALCOHOL PRIMARY AMINE A 1,4-cyclohexane-tert-octylamine dimethanol B 1,4-cyclohexane- 2-ethylhexylaminedimethanol C 2,2-dimethyl-1,3-propane 2-ethylhexylamine diol Dtriethylene glycol tert-octylamine E tripropylene glycol2-ethylhexylamine F tripropylene glycoI cyclohexylamine G tripropyleneglycol tert-octylamine

Preparation of Polyurethanes

One equivalent of the chain extender indicated in Table 2 was combinedwith 1 equivalent of the isocyanate indicated in Table 2. The reactiontime reported in Table 2 is the amount of time necessary for theisocyanate formulation to reach a viscosity above 2,000 mPa·s (at 25°C.).

TABLE 2 CHAIN EXAMPLE ISOCYANATE EXTENDER REACTION TIME 1 HDI¹2-methyl-1,5- <1 second pentane diamine² 2 HDI¹ A 35 seconds 3 HDI¹ B 10seconds 4 HDI¹ C 40 seconds 5 HDI¹ D 40 seconds 6 HDI¹ E 45 seconds 7HDI¹ F 20 seconds 8 HDI¹ G 21 minutes 9 TDI³ D 15 seconds 10  TDI³ F 90seconds ¹Hexamethylene diisocyanate which is commercially available fromBayer Corporation under the name Desmodur N3300. ²Commercially availablefrom DuPont under the name Dytek A. ³Toluene diisocyanate which iscommercially available from Bayer Corporation under the name MondurTD-80.

Example 1 illustrates a chain extender having primary amine groups. Thesignificance of the primary amine group is evident from the reactiontime for the formulation of Example 1 as compared to the reaction timesfor the secondary amine chain extenders within the scope of the presentinvention.

The reaction times reported in Table 2 also indicate that the moresteric hindrance in the chain extender, the longer the reaction time.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

What is claimed is:
 1. A process for controlling pot life of anisocyanate formulation comprising including a chain extender having a)at least two secondary amine groups, b) no primary amine group, and c) areactivity low enough that the chain extender will not reactsufficiently with isocyanate groups present in the isocyanateformulation to increase the viscosity of the isocyanate formulation tomore than 2000 mPa·s within 5 seconds in the isocyanate formulation inan amount such that the desired pot life is attained.
 2. The process ofclaim 1 in which the chain extender has secondary amine groups which donot react with isocyanate groups present in the isocyanate formulationsufficiently to increase viscosity of the isocyanate formulation togreater than 2000 mPa·s for at least 10 seconds.
 3. The process of claim1 in which the chain extender is represented by the formulaR¹NR²—X—NR³R⁴  (I) in which R¹ represents an alkyl group having from 1to 18 carbon atoms, a cycloalkyl group having from 3 to 18 carbon atomsor an aryl group having from 4 to 18 carbon atoms, R² representshydrogen, R³ represents an alkyl group having from 1 to 18 carbon atoms,a cycloalkyl group having from 3 to 18 carbon atoms or an aryl grouphaving from 4 to 18 carbon atoms, R⁴ represents hydrogen, and Xrepresents an alkyl group having from 1 to 16 carbon atoms, an arylgroup having from 6 to 14 carbon atoms, or an ether group composed of atleast one oxygen and two carbon atoms.
 4. The process of claim 3 inwhich in formula (I) R¹ represents an alkyl group having from 1 to 8carbon atoms or a cyclohexyl group, R² represents hydrogen, R³represents an alkyl group having from 1 to 8 carbon atoms or acyclohexyl group, R⁴ represents hydrogen, and X represents the residueof 1,4-cyclohexanedimethanol, 2,2-dimethyl-1,3-propanediol, triethyleneglycol or tripropylene glycol.
 5. The process of claim 3 in which theviscosity of the isocyanate formulation containing the amine chainextender does not reach 2,000 mPa·s for a period of at least 10 seconds.6. The process of claim 1 in which the isocyanate in the isocyanateformulation is toluene diisocyanate.
 7. The process of claim 1 in whichthe isocyanate in the isocyanate formulation is hexamethylenediisocyanate.